The paper deals with the tray efficiency estimation in the presence of entrainment, using one-parametric diffusion model for the column as a whole. The case of mass transfer in the trayed column accompanied by intensive entrainment of liquid is analysed, when both equilibrium and 'dry working regime' operating lines are straight. Using proposed algorithm it is possible to determine the number of actual trays in the column based on the inlet and outlet concentrations in one phase, inlet concentration in the other phase and the characteristics of mass transfer at trays. The obtained equations present the broadening of well-known Kremser equations.